Twinkle, twinkle - astronomers find ‘smallest ever’ star

Rob Waugh
University of Cambridge

Our own sun is 330,000 times the weight of our planet, and so big that more than a million Earths could fit inside it – but not every star is quite so large.

Astronomers at the University of Cambridge have discovered the smallest star ever measured – and probably about the smallest there is.

The planet is just a shade bigger than Saturn – and its gravity is only 300 times stronger than what we feel on Earth.

The newly-measured star, called EBLM J0555-57Ab, is located about six hundred light years away.

The star is likely as small as stars can possibly become, as it has just enough mass to enable the fusion of hydrogen nuclei into helium – the fusion which powers the Sun.

If it were any smaller, the pressure at the centre of the star would no longer be sufficient to
enable this process to take place.

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These small dim stars could be good candidates for detecting Earth-sized planets which can have liquid water on their surfaces, such as TRAPPIST-1 an ultracool dwarf surrounded by seven temperate Earth-sized worlds.

It is part of a binary system, and was identified as it passed in front of its much larger companion, a method which is usually used to detect planets, not stars.

‘Our discovery reveals how small stars can be,’ said Alexander Boetticher, the lead author of the study, and a Master’s student at Cambridge’s Cavendish Laboratory and Institute of Astronomy.

‘Had this star formed with only a slightly lower mass, the fusion reaction of hydrogen in its core could not be sustained, and the star would instead have transformed into a brown dwarf.’

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